The use of sensing devices in anatomical lumens is well known. For example, U.S. Pat. No. 4,485,813 describes a cardiac pacemaker sensor that can be permanently implanted in a specific location within a patient's body. U.S. Pat. Nos. 6,645,143, 6,053,873, and 6,442,413 and U.S. Patent Publication No. 2002/0188207 describe medical monitoring sensors designed to be permanently implanted in blood vessels and capable of sensing and transmitting via a telemetry link to an external monitor. The implanted sensing devices are utilized for monitoring physiological parameters within the patient's body.
Because the force created by the blood flow and/or heart movement, which may act on an implanted sensing device like a sail, tends to drag the sensing device longitudinally along the vessel, or rotate it in the case where the sensing device is implanted adjacent a bifurcation of a vessel branch, it is critical that the anchoring force created between the sensing device and the wall of the blood vessel be as great as possible. However, high local or radial force on the relative weak pulmonary artery vessel wall may cause perforation or aneurysm. Many of the vascular implantation techniques assume that the segment of the blood vessel in which the sensing device is intended to be implanted is straight (i.e., it has no branches). In some cases, however, the vessel segment may be branched. If the vessel segment adjacent the branch is long enough to accommodate the entire length of the sensing device, the sensing device may be implanted within the blood vessel without regard to the branch. If, however, the length of the vessel segment is limited, the sensing device may not be adequately implanted within the vessel segment without crossing the branch. In this case, the implanted sensing device may block future access to the vessel branch, e.g., during catheterization, may be unstable due to the transverse blood flow through the branch, and worse yet, may cause blood clots that may potentially result in an embolism. As a result, the length of the sensing device sufficient for affixation to the wall of the blood vessel may have to be reduced in order to accommodate the branched vessel. In addition, the diameters of many blood vessels are not uniform, and may even be conical, thereby presenting further challenges to lengthening the sensing device.
The right pulmonary artery, which is frequently the target of sensor implantation, such as for the purpose of monitoring hemodynamic parameters indicative of the efficiency of the heart or measure the glucose level of the blood, is both branched and non-uniform. For example, referring to FIG. 1, an implantable sensing device 10, which generally includes a fixation element 12 (e.g., a stent) and a sensing element 14 coupled to the fixation element 12, is shown implanted within the right pulmonary artery RPA of a patient. As shown by the arrows, blood flows from the right ventricle RV of the heart, out through the main pulmonary artery MPA, which branches into the right pulmonary artery RPA and a left pulmonary artery LPA. The sensing element 14, once implanted, may thus be capable of monitoring, e.g., the hemodynamic parameters of the blood flowing from the right ventricle RV.
As can be seen in FIG. 1, the right pulmonary artery RPA branches into various side branches SBR, none of which is crossed by the sensing device 10 to prevent the afore-mentioned problems from occurring. However, because the length of the implantable segment of the right pulmonary artery RPA (i.e., the segment between the point at which the right pulmonary artery RPA begins and the point at which the first side branch SBR, known anatomically as “Truncus anterior”, begins) is relatively short (on average, about 40 mm), the length of the fixation element 12 must be relative short in order to accommodate the side branch SBR.
Because the length of the fixation element 12 must be relatively short, the stability of the sensing device 10 may be compromised. In addition, as can be seen from FIG. 1, the diameter of the right pulmonary artery RPA substantially decreases in the distal direction (i.e., from right to left), which causes the proximal end of the fixation element 12 to engage the vessel wall less firmly than the distal end of the fixation element 12 engages the vessel wall, thereby further compromising the stability of the sensing device 10.
There, thus, is a need to provide an improved technique for implanting a sensing device in a non-uniform and branched anatomical vessel.